Motor fuel



3,098,470 Patented July 23, 1963 fiice 3,998,470 MOTOR FUEL Fred K.Kawahara, Park Forest, 111., assignor to Standard Oil Company, Chicago,11]., a corporation of Indiana No Drawing. Filed Feb. 27, 1959, Ser. No.795,893 9 Claims. (Cl. 123-1} This invention relates to motor fuelscharacterized by their ability to suppress surface ignition in theoperation of internal combustion engines. More particularly, theinvention provides an improved motor fuel which is effective insuppressing surface ignition or preignition.

Current emphasis on high compression ratios and other high-performancedesign features in gasoline engines of the internal combustion type hascreated a situation Where random knock from surface ignition, oftenreferred to as preignition," has become a limiting factor in enginedesign and operation. Knock induced by surface ignition appears to be aresult of the use of organo-lead compounds, particularly tetraethyllead, as the anti-knock agent in high octane number fuels. When leadedmotor fuels are burned in internal combustion engines, deposits ofcarbonaceops material and lead salts are continuously formed on thecombustion chamber walls. Apparently surface ignition, that is, theignition of the fuel-air mixture either before or after passage of thespark, is caused by glowing of carbon in the deposits. It is generallybelieved that the presence of lead compounds in the deposits causes thecarbon to glow at a significantly lower temperature than the glow pointof carbon alone.

'It is well known that the addition of certain organic compounds ofphosphorus, such as tricresylphosphate, to leaded fuels results inreducing surface ignition. Unfortunately, phosphorus compounds varywidely in effectiveness, and those that are most effective often havethe undesirable property of lowering the octane number of the fuel. Withpetroleum refiners spending millions of dollars annually to raise theoctane numbers of premium motor fuels, any substantial decrease inoctane number is of course intolerable.

In accordance with the invention, an additive for use with leaded motorfuels has now been discovered which is extremely effective in reducingsurface ignition or preignition," yet, when employed in properquantities, does not substantially reduce the octane number of the fuel.Specifically, it has now been discovered that thioesters of a cyclicdithiophosphoric acid, having the formula wherein the Y groups are eachhydrogen atoms or alkyl radicals of 1-4 carbon atoms each, and X is analkyl, aryl, aralkyl, or alkaryl radical having up to about 15 carbonatoms per radical, are outstanding preignition suppressant additiveswhen incorporated into leaded gasolines in an amount sufficient toprovide a mol ratio of phosphorus to lead of from about 0.01 to about1.0. Preferably, the molar ratio of phosphorus to lead (MR P/Pb) is inthe range of 0.020.20.

It has further been discovered, contrary to experience with most otherorganic compounds of phosphorus, that the inventive additives act aseffective gasoline antioxi dants, and hence reduce the tendency of themotor fuel to form gums in storage. In addition, they do not cause fuelinduction system deposits and they virtually eliminate sticking ofengine intake and exhaust valves.

The motor fuel of the invention may contain tetraethyl lead equivalentto a concentration of from about 0.5 ml. to about 5 ml. or more pergallon of the hydrocarbon motor fuel; the concentration of tetraethyllead may be varied as is usual with the engine and its use.

The hydrocarbon component which constitutes the base of the fuel willpreferably be gasoline but may be any other combustible liquid ofsuitable volatility commonly employed as fuel for internal-combustionspark ignition engines, including parafiinic, naphthenic and aromatichydrocarbons, pure hydrocarbons such as isooctane, and mixtures ofisooctane with other suitable liquid hydrocarbons. These fuels may bederived, in whole or in part, by distillation of crude oil, catalytic orthermal cracking of gas oils, alkylation of isoparaliins with olefins,polymerization of olefins, etc. The boiling point of such fuels shouldbe in the range of about F to about 500 F. and preferably in the rangeof about F. to about 400 F. Motor fuels may also contain anti-oxidants,stabilizers, dyes, antiicing agents, halogen-type lead scavenging agentsand/or other compounds which are commonly employed in leaded motorfuels.

There can also be provided, in accordance with the invention, anadditive concentrate suitable for incorporation into leaded motor fuelswhich contains a substantial amount (1-l00%) of the above describedthioester of disubstituted thiophosphoric acid. Thioester concentrationsof 5-85 wt. percent are preferred. The additive concentrate may alsocontain an inert solvent, such as a refined hydrocarbon oil, and alsodesirable amounts of tetraethyl lead (to provide an MR P/Pb in the rangeof (101-11)), halo-hydrocarbon lead scavenging agents, dyes, and thelike.

The defined additives, which are thioesters of a cyclic disubstituteddithiophosphoric acid, may be prepared by any of the conventional meansknown for preparing analogous thioesters. Thus, appropriate diols,having two carbinol groups separated by a single carbon atom, may bereacted with phosphorus pentasulfide (P 8 to form a cyclicdithiophosphoric acid, and then reacted with a halide of the radical (X)to be introduced. Typical examples of appropriate diols include2-methylpentanediol-2,4, propanediol-l,3, butanediol-l,3,2-ethylhexanediol-L3, pentanediol-2,4, etc. Although the Y groups on thepreviously-defined structural formula may be hydrogen atoms or alkylradicals of l-4 carbon atoms, it is preferred that there be at least onealkyl radical of l-3 carbon atoms on at least two of the carbon atomswhich ultimately form the cyclic structure. For instance,2-methylpentanediol- 2,4 reacts with P 8 to form 1,1,3-trimethyl cyclotrimethylene thiophosphoric acid, which can then be reacted with, say,benzyl chloride to form the benzyl dithiophosphate. This method isespecially suitable for aryl and aralkyl groups such as phenyl, tolyl,ethylphenyl, etc.

It is preferred, for reasons of convenience and economy, to react thecyclic dithiophosphorie acid with an olefinic hydrocarbon having up to15 carbon atoms per molecule to form the inventive additive. Aspreviously mentioned, the X group may be alkyl, aryl, aralkyl, oralkaryl, and accordingly the olefinic hydrocarbon can be any compoundwhich alfords such group. Among the suitable compounds which can formthe X group of the defined formula are ethylene, propylene, i-butylene,heXene-l, heptene-l, i-octenes, decenes, cyclopentene; styrene, amethylstyrene, dimethyl-B-methyl styrene, p-t-butyl styrene, and otheraralkenes of 7-15 (more desirably 7-10) carbon atoms. Using thestyrenes, it is believed that the sulfur atom attaches to the or carbonatom of the styrene.

As specific embodiments of the invention, the following examples aregiven. It is to be understood that these are by way of illustration onlyand are not intended as a limitation of the invention:

3 EXAMPLE I In this example, 1,1,3-trimethyl cyclo trimethyleneaphenylethyl dithiophosphate was prepared in a one-step process. To amixture of styrene (1.1 mols) and 2-methylpentane diol-2,4 (1.2 mols),phosphorus pentasulfide (0.5 mol) was added gradually at l65-l90 F. overa 1- hour period. The mixture then was permitted to react for 2 hours at210 F. and was then purified by filtration through filter paper.Cryoscopic examination of the product after water washing and drying atreduced pressure showed it to be essentially the monomer.

Analysis.-Calcd.: phosphorus, 8.95 wt. percent; sulfur, 18.3%. Found:phosphorus, 8.80 wt. percent; sulfur, 16.93%.

EXAMPLE II In this example, a two-step reaction was employed to prepare1,1,3-trimethyl cyclo trimethylene a-phenylethyl dithiophosphate. Thereaction was conducted by adding 111 grams (0.5 mol) of P 5 to 130 grams(1.11 mols) of 2-methylpentanediol-2,4 gradually during two hours, andthen adding 124 grams (1.2 mols) of styrene in 1% hours at 195 F. Themixture was then diluted with 88 grams of 5-W oil and 200 grams ofxylene solvent.

EXAMPLE III In this example, l-methyl cyclo trimethylene a-phenylethyldithiophosphate was prepared. To a mixture of 216 grams (2.4 mols) ofbutanediol-l,3 and 228.8 grams (2.2 mols) of styrene, there was added222 grams (1 mol) P 5 at 170190 F. over a one-hour period. The reactionmixture was then heated at 220 F. for a five-hour period. 633.3 grams ofproduct was recovered; it analyzed 9.81 wt. percent phosphorus.

EXAMPLE IV In this example, 1,1,3-trimethyl cyclo trimethylene heptyldithiophosphate was prepared. To a mixture of 141 grams (1.2 mols)Z-methyl pentanediol-2,4 and 216 grams (2.2 mols) of technical or mixedheptenes, there was added 111 grams (0.5 mol) P 5 gradually over a 55-minute period at l58-168 F. The reaction mixture was then heated at190-l95 F. for three hours. 442 grams of product was recovered; itanalyzed 7.04% P, 14.8% S,

and had an acid number of 9 (mg. KOH/g.).

EXAMPLE V Test duration 50 hours.

Coolant temperature 148 F. Oil temperature 160 F. Air to fuel ratio13/1. For this test the engine is cycled as follows:

Cycle Conditions 45 135 600 900 None Full Surface ignition preventioneffectiveness was determined using a premium fuel having 3 cc. of TELper gallon and incorporated therewith the inventive additive and otherphosphorus compounds.

EFFECTIVENESS IN SUPPRESSING SUFACE IGNITION CFILF HEAD ENGINEConcentration, MR PJPb Additive 1 A hydrocarbon dithiophosphate.

The test data in the above table demonstrate the superiority of thepresent additive over other phosphorus compounds with respect to surfaceignition control. It will be noted that the additive may be employed atonefourth to one-half the concentration of hitherto well knownpreignition suppressants.

It was previously indicated that a major advantage of the inventiveadditive is in its ability to be incorporated into high octane gasolineswithout substantially reducing the octane number of said gasolines. Todemonstrate this, tests were made in a CFRL head engine at variousconcentrations of several additives in a 9394 octane number motor fuel,containing 3.0 cc. TEL per gallon. The following results were observed.

A surprising benefit attendant with the present additives is theirability to function as antioxidants to prevent oxidative gum formationin the gasoline on long term storage. This was demonstrated by testingmotor fuels at accelerated storage conditions of 212 F. and p.s.i.g.oxygen pressure, and noting the time (induction period) before rapidoxygen consumption occurred. The following results were observed withthe additive of Example I:

Additive concentration: Induction period, minutes Nil 325 0.13 MR P/Pb390 0.33 490 The additive of Example I was also tested for itsequilibrium octane performance in a 1953 Oldsmobile V8 engine havingspecial 10:1 compression ratio heads, under the following conditions:

Speed, r.p.m 1500 Load, B.H.P 9.5 Coolant Temp. F 175 Oil temp., F 165Air-intake temp., F 100 Air-fuel ratio 13:1 Spark advance, BTDC 11 Onceeach hour the engine was operated at full-throttle, 1500 r.p.m.80 B.H.P.for 15 seconds. The equilibrium octane requirements and octanerequirement increase (ORI) of the engine were determined after hours andafter 300 hours of operation and are shown below.

OOTANE REQUIREMENT INCREASE The inventive compositions are outstandingwith respect to their ability to prolong exhaust valve life, in markedcontrast to the deleterious elicct which many other phosphorus compoundshave. To illustrate this, tests were made on 1953 Chevrolet engineshaving a 216 cubic inch displacement and operated under the followingconditions:

Speed, r.p.m 2,500 Load, B.H.P 25-45 Coolant temperature, F 165 Oiltemperature, F 200 Air-fuel ratio 16:1 Spark advance, BTDC 32 Spark gap,inches 0.040 Exhaust valve clearance, inches 0.020 Manifold vacuum,inches Hg 7 At the end of 50 hours of testing, the engines were examinedand the following results observed:

EXHAUST VALVE INSPECTION Additive Concentration Exhaust valve conditionNone Four stuck. Example 1 0.13 MB P/Pb All good.

The engines were disassembled and visually inspected for inductionsystem deposits; both passed.

The additive of Example I was exposed to the copper strip test, whichconsists of placing a clean copper strip in a sample of motor fuelcontaining the additive at 122 F., and examining the strip after threehours. At concentrations of 0.13 and 0.33 MR P/Pb, the strip had thesame good color as the blank (zero additive concentration).

The additive of Example I also exerts a powerful action on maintainingspark plugs in clean, unfouled condition. In tests on an Oldsmobileengine, the following results were observed:

SPARK PLUG LIFE The percentages given herein and in the appended claimsare weight percentages unless otherwise noted.

While the invention has been described by reference to specificembodiments thereof, the same are given by way of illustration.Modifications and variations will be apparent to those skilled in theart.

We claim:

1. A hydrocanbon motor due] of the gasoline boiling range adapted forspark-ignition internal-combustion engines, containing a minor amount oftetraethyl lead and, in combination therewith, in an amount sufficientto provide a mol ratio of phosphorus to lead of from about 0.01 to about1.0, a thioester of a cyclic dithiophosphoric acid having the formulawherein the Y groups are each selected from the group consisting ofhydrogen atoms and alkyl radicals of 1-4 carbon atoms each, and X isseiected from the group consisting of alkyl, aryi, aralkyl, and alkarylradicals having up to about 15 carbon atoms.

2. The fuel of claim 1 wherein the minor amount of tetraiethyl lead isin the range of about 0.5 to about 5.0 cc. per gallon of incl.

3. The fuel of claim 1 wherein Y Y and Y are methyl radicals and Y Y andY are hydrogen atoms.

4. The fuel of claim 1 wherein X is a phenylethyl radical.

5. The fuel of claim 1 wherein X is a heptyl radical.

6. The fuel of claim 1 wherein X is a di-i-butylene radical.

7. A hydrocarbon mot-or fuel of the gasoline iboiling range adapted forspark-ignition internal-combustion en- .gines containing from 0.5 to 5.0cc. tetraethyl lead per gallon of fuel, and, in an amount sutficient toprovide a mol ratio of phosphorus to lead of from about 0.01 to about1.0, 1,1,3 trimethyl cyclic trimethylene phenylethyl dithiophosphate.

8. An additive concentrate composition suitable for incorporation inleaded hydrocarbon motor fuels of the gasoline boiling range adapted forspark-ignition internal-combustion engines, said additive concentratecomposition consisting essentially of tetraethyl lead and a substantialamount of a thioester of a cyclic dithiophosphoric acid having theformula wherein the Y groups are each selected from the group consistingof hydrogen atoms and alkyl radicals of 1-4 carbon atoms each, and X isselected from the group consisting of alkyl, aryl, aralkyl, and alkaryiradicals up to about 15 carbon atoms.

9. In the method of operating sparkignition internal combustion engines,the improvement which comprises supplying to said engines a hydrocarbonmotor fuel of the gasoline lbioiling range containing a minor amount ofrtctraethyl lead and, in combination therewith, in an amount suliicientto provide a mol ratio of phosphorus to lead of from about 0.01 to about1.0, a tthi-oester of a cyclic dithiophosphoric acid having the formulawherein the Y groups are each selected from the group consisting ofhydrogen atoms and alkyl radicals of 1-4 carbon atoms each, and X isselected from the group consisting of alkyl, aryl, aralkyl, and alkarylradicals having up to about 15 carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS2,737,932 Thomas Mar. 13, 1956 2,794,719 Bartleson June 4, 19572,794,720 Bartleson June 4, 1957 2,892,691 Howell June 30, 19592,892,863 Lanham June 30, 1959 2,894,016 Laniham July 7, 1959 2,897,071Gilbert July 28, 1959 2,902,983 Patbeng Sept. 8, 1959

9. IN THE METHOD OF OPERATING SPARK-IGNITION INTEGRAL COMBUSTIONENGINES, THE IMPROVEMENT WHICH COMPRISES SUPPLYING TO SAID ENGINES AHYDROCARBON MOTOR FUEL OF THE GASOLINE BOILING RANGE CONTAINING A MINORAMOUNT OF TETRAETHYL LEAD AND, IN COMBINATION THEREWITH, IN AN AMOUNTSUFFICIENT TO PROVIDE A MOL RATIO OF PHOSPHORUS TO LEAD OF FROM ABOUT0.01 TO ABOUT 1.0, A THISOESTER OF A CYCLIC DITHIOPHOSPHORIC ACID HAVINGTHE FORMULA